Quantitation of Four Tryptophan-Related Impurities in Compound Amino Acid Injection-18 AA by HPLC–PDA

Compound amino acid injection-18 AA (CAAI-18 AA) is widely applied in medical care as a part of total parenteral nutrition systems. Thus, suitable quality control of CAAI-18 AA is of crucial importance for safety of the patients. Tryptophan (TRP) is one of the main components in CAAI-18 AA and may be degraded to 5-hydroxy-tryptophan (5-HTP), 5-hydroxytryptamine (5-HT), kynurenine (KYN) and indole (IN) under certain conditions, such as oxidation environments, ultraviolet light radiation and nonsterile conditions. The existence of these harmful impurities seriously affects the quality of CAAI-18 AA. Here, a simple HPLC approach with a PDA detector was developed and validated for simultaneous determination of the concentrations of 5-HTP, 5-HT, KYN and IN impurities in CAAI-18 AA. Separation of these four impurities in CAAI-18 AA was achieved under a gradient condition using acetonitrile and 10 mM phosphate buffer (containing 10 mM sodium 1-octanesulfonate, pH adjusted to 1.8 with phosphoric acid). To detect the four analytes with high sensitivity, multi-wavelength detection at 257, 270 and 276 nm was carried out during the separation. The method was validated in accordance with ICH guidelines and the results were compared to that obtained by UHPLC–MS/MS, showing that the two approaches did not provide significantly different results. Our results reveal that the simple and less expensive HPLC method holds great potential for quantitation of the four impurities in CAAI-18 AA. Graphic Abstract